The invention relates to a transmission for an internal combustion engine including an oil sump and an oil pump for pumping oil from the oil sump through a lubricating circuit.
Transmissions for internal combustion engines with an oil sump and an oil pump for a main oil supply circuit are known in the art. For the parts of the transmission, which are immersed into the oil sump, lubrication is provided by the oil of the oil sump. For the parts of the transmission which do not extend into the oil sump, a main oil circuit is provided for lubrication. The main oil circuit includes an oil pipe and a pump operatively in communication with the oil sump and the oil pipe for supplying oil from the oil sump through the oil pipe to various lubricating points. The oil sump includes a predetermined amount of oil, which is constantly circulated by contact with the moving parts extending into the oil sump and by the oil pump.
It is the object of the present invention to provide a transmission in which the friction forces generated by operation of transmission parts immersed in the oil is minimized.
In a transmission for an internal combustion engine including an oil sump forming an oil reservoir and an oil pump operatively in communication with the oil sump, an additional oil reservoir is provided for receiving oil from the oil sump when the transmission is in direct drive and power is transmitted only through the main shaft of the transmission while the intermediate shaft is idling so that no friction is generated by the gears of the intermediate shaft being immersed in the oil of the oil sump.
With this arrangement, the oil level in the transmission can be adjusted dependent on the respective operating stages of the transmission. At any point, the oil level in the transmission can be reduced to avoid splash losses as much as possible.
To this end, it is advantageous if, in addition to the oil sump and the main oil circuit, at least one dry sump oil circuit is provided and the dry sump oil circuit is operatively connected to a main shaft and the main oil circuit is connected to the gears and/or the intermediate shaft and/or an oil cooling system. In this way, the transmission components which are disposed in the power transmission path, but which are not lubricated directly by the oil in the oil sump when the oil level is lowered, can still be lubricated as needed. It is furthermore possible to appropriately lubricate also those transmission components, which are always disposed above the oil sump.
It is furthermore advantageous to provide, in addition to the oil pump, at least a second oil pump or to provide a variable volume oil pump or at least a two stage oil pump wherein the pump ratio of the oil pump to the second oil pump or the ratio between the stages is between 1.3 and 3. The oil sump and/or the additional oil storage is operatively connected to at least one of the oil pumps. When the oil level is lowered, the dry sump circuit also has to be activated. With two oil pumps or, respectively, a two-stage oil pump, the oil level can be rapidly lowered while, at the same time, the dry sump circuit is supplied with oil. It is noted that the oil supplied to the dry sump circuit returns to the oil sump after lubricating the transmission components, that is, it acts in opposition to the lowering of the oil level in the oil sump. The pumping ratio should therefore assume the highest possible value so that the oil intake of the pump is substantially larger than the volume flow of the dry sump circuit, which returns again to the oil sump.
In connection with the present invention, it is particularly important that the oil reserve is limited or determined by at least a web or a wall arranged in the oil sump at the bottom of the transmission and that a controllable compensating valve is disposed between the oil sump and the oil reservoir.
When, after an oil level-lowering phase, the oil level is raised, oil can flow through the compensating valve connection so as to hasten the filling of the oil sump beyond that achievable by way of the pump. The compensation valve is arranged in this case within the web in order to facilitate the compensation flow between the oil reservoir oil and the sump.
In connection with the arrangement according to the invention, it is advantageous if at least one gear disposed in oil provides for movement of the oil in the sump toward the oil reservoir. In this way, a second pump is not necessary. The oil reservoir is constantly filled by the oil movement or pumping action of the shaft or gears. This pumping power is constant, so that, for filling the oil sump by way of the compensating valve or the pump, the transport volume of the gear can be compensated for. When the compensation valve is opened, the pumping of the gears has only a relatively small effect on the oil level in the oil sump, which is constantly filled by way of the compensation valve and the pump.
It is further advantageous if the second oil pump is in operational communication with the oil reservoir and the dry sump circuit is and the oil pump are in communication with the oil sump, and, by way of a valve, with the main oil circuit or with a supply line for the oil reservoir. When the oil level in the oil sump is at low levels, the second oil pump supplies oil to the dry sump circuit from the oil reservoir. The oil pump, which, at normal oil levels in the oil sump, supplies oil to the main oil circuit which has already been described, is employed to pump oil from the oil sump, to which the oil from the dry sump circuit returns, to the oil reservoir. Via the valve, the oil pump is either switched into the main oil circuit or into the supply circuit for supplying oil to the reservoir.
It is furthermore advantageous that the oil pump is in communication with the oil reservoir and, by way of the valve, with the main oil circuit and/or with the dry sump circuit. If only one oil pump is used, the oil reservoir is replenished by means of a gear. The oil pump is used for supplying oil from the oil reservoir to the dry sump circuit and/or the main oil circuit, depending on the position of the valve. The oil level in the oil reservoir is at least as high as that in the oil sump even when the compensation valve is open.
It is furthermore advantageous that, when the transmission is in direct gear or at an optimal operating point, the oil level in the transmission is lowered and part of the oil is supplied by the oil pump and/or the rotating gears into the oil reservoir. The constants and the main shaft are lubricated by way of the dry sump circuit. A main oil circuit, which is in communication with the gears and/or with the intermediate shaft and/or with the oil cooling system, is selectively inactive. Upon engaging a gear different from the direct gear, the oil reservoir is placed by the compensation valve in communication with the oil sump and the oil level in the oil reservoir is again raised. At the same time, the main oil circuit, which is in operational communication with the gears and/or with the intermediate shaft and/or the oil cooling system, is activated.